Thermoelectric device

Abstract

The present invention is a thermoelectric device comprising: a thermoelectric element composed of principally thermoelectric material, a counter element adhered to said thermoelectric material, a solder layer lying between said thermoelectric element and said counter element and adhering said thermoelectric element to said counter element, a restraining layer to prevent said solder's ingredient of said solder layer from spreading into said thermoelectric element, wherein said restraining layer comprising a first layer to prevent said solder's ingredient of said solder layer from spreading into said thermoelectric element and a second layer composed of material which gets wetter than said first layer against said solder layer.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a thermoelectric device comprising a thermoelectric element composed of principally thermoelectric material.

[0003] 2. Discussion of the Background

[0004] The thermoelectric device comprising a thermoelectric element principally composed of thermoelectric material is well known in the art.

[0005] The thermoelectric device has two types of usages one is a cool-heat type which can cool or heat when electricity being supplied, and the other is a power generation type which can generate electricity when being cooled or heated.

[0006] A known conventional thermoelectric device is disclosed in pages 24 to 25 of “thermoelectric transfer system technical general handbook” published by realize company published date; on June 30, June, 1995 (heisei 7).

[0007] The nickel plating layer prevents the solder's ingredient of said solder layer from spreading into the thermoelectric element, and consists of a single layer. According to the conventional thermoelectric device, the nickel plating layer prevents the solder's ingredient of the solder from spreading into said thermoelectric element. Therefore, the conventional thermoelectric device has advantages of restrained degradation of thermoelectric device and maintained characteristic of thermoelectric device for long term.

[0008] Furthermore, in general, the thermoelectric element composed of thermoelectric material is hard to be soldered. The nickel plating layer has an advantage to prevent the solder's ingredient of the solder layer from spreading into the thermoelectric element, and improve a soldering characteristic of the thermoelectric element when the thermoelectric element being assembled.

[0009] In the industry, the higher characteristic of restraining spread prevention and soldering are requested. However, the single nickel plating layer needs more improvement in aspect of combining two higher characteristics of spread prevention and soldering. In other words, if the nickel plating layer is used for high characteristic of spread prevention, it has an advantage to prevent solder's ingredient of the solder layer from spreading into the inside of the thermoelectric element, but then it has disadvantage to get insufficient increase wetting property against the solder. Contrary, if the nickel plating layer is used for the high wetting property against the solder, it is not sufficient to increase the increasing of the characteristic of spread prevention.

[0010] An object of the present invention is to solve the above-mentioned disadvantages, and more specifically, to provide a thermoelectric device having both improvements for better soldering property and spread prevention.

SUMMARY OF THE INVENTION

[0011] The present invention is a thermoelectric device comprising: a thermoelectric element composed of principally thermoelectric material, a counter element adhered to said thermoelectric material, a solder layer lying between said thermoelectric element and said counter element and adhering said thermoelectric element to said counter element, a restraining layer to prevent said solder's ingredient of said solder layer from spreading into said thermoelectric element, wherein said restraining layer composed a first layer to restrain what said solder's ingredient of said solder layer spreads into said thermoelectric element and a second layer composing of material which gets wetter than said first layer against said solder layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above and other objects, features and advantages of the present invention will be more apparent and more readily appreciated from the following detailed description of preferred exemplary embodiments of the present invention, taken in connection with the accompanying drawings, in which:

[0013] FIG. 1 is front view showing an outline structure of a thermoelectric device according to an embodiment of the present invention.

[0014] FIG. 2 is a schematic cross sectional view of substantial part of a thermoelectric device according to the embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] According to the present invention, the thermoelectric material for the thermoelectric device is at least one of selected from bismuth-tellurium series, bismuth-selenium series, antimony-tellurium series, antimony-selenium series, bismuth-tellurium-antimony series, and bismuth-tellurium-selenium series. Specifically, it is at least one of selected from Bi2Te3, Bi2Se3, Sb2Te3, Sb2Se3. Bismuth-tellurium-antimony series is selected for a thermoelectric device of P-type (positive type). Bismuth-tellurium series and bismuth-tellurium-selenium series are selected for a thermoelectric device of N-type (negative type).

[0016] According to the present invention, the counter element adhered to the thermoelectric element is a substrate having an electrode. A ceramic substrate may be employed for the substrate. A ceramic material is selected from alumina series, aluminum nitride series, beryllia (BeO) series, and silicon carbide series etc. A solder may be selected from bismuth-tin series, tin-antimony series, lead-tin series, lead-tin-bismuth series, tin series, and lead series etc., but the solder is not limited to aforementioned series.

[0017] According to the present invention, the restraining layer comprises a first layer to prevent the solder's ingredient of said solder layer from spreading into the thermoelectric element and a second layer composed of material which gets wetter against the solder layer than the first layer. The first layer is nonelectrolytic plating layer composed of nickel-phosphorus series, or non-electrolytic plating layer composed of nickel series. The second layer has preferably both improvements of wetting property against the solder. A second layer comprised a non-electrolytic plating layer composing of nickel-boron series. A non-electrolytic plating layer composed of nickel-boron series is slower in the plating speed and more expensive in manufacturing than a non-electrolytic plating layer composed of nickel-phosphorus series. However, nickel-boron has excellent wetting property against the solder when soldering, so that the soldering characteristic of the thermoelectric device is improved.

[0018] A non-electrolytic plating layer composed of nickel-phosphorus series is a little degradation in the wetting property, but is faster in the plating speed and cheaper in manufacturing than a nonelectrolytic plating layer composing of nickel-boron series.

[0019] A non-electrolytic plating layer composing of nickel-phosphorus series is produced by the plating bath including, but not limited to nickel-chloride or hydrosulfate, with sodium hypophosphite as the reducer. A non-electrolytic plating layer composing of nickel-boron series is produced by plate bath including, but not limited to, nickel-chloride or hydrosulfate with boron hydroxylase as the reducer.

[0020] In some cases, the first layer and the second layer do not limited by non-electrolytic plating, and these can be produced by electroplating of nickel metal etc.

[0021] According to the present invention, the average thickness of the first layer is thicker than that of the second layer to increase the spread prevention effect at low cost by the short time process. Though a ratio of the average thickness between the first layer, and the second layer is varied by consideration of manufacturing speed or manufacturing cost under usable conditions, it may be settled for “the average of the first layer: the average of the second layer=1: (1 to 300)”. Preferably, it may be settled for “the average of the first layer: the average of the second layer=1: (1 to 100)”. More preferably, it may be settled for “the average of the first layer: the average of the second layer=1: (2 to 10)”. However, the present invention is limited by the aforementioned.

[0022] A ratio of raw value of the average thickness between the first layer and the second layer is varied by consideration of manufacturing speed, manufacturing cost under usable conditions, or material of the first layer or the second layer etc. Accordingly, in some cases, for example, the average of the first layer is settled for 0.2 to 50 &mgr;m, 0.5 to 20 &mgr;m, 1.0 to 15 &mgr;m, 1.0 to 10 &mgr;m, and 5 to 10 &mgr;m etc. The average of the second layer is settled for 0.04 to 10 &mgr;m, 0.8 to 5 &mgr;m, 0.1 to 1.0 &mgr;m, and 0.1 to 0.5 &mgr;m etc. However, the present invention is not limited by the aforementioned ratio of them.

EMBODIMENT EXAMPLE

[0023] Preferred embodiments of the present invention will be described hereinafter in detail with reference to the accompanying drawings.

[0024] FIG. 1 is a front view showing an outline structure of a thermoelectric device according to the embodiment of the present invention. FIG. 2 is schematic cross sectional view of a thermoelectric device according to the embodiment of the present invention. As shown in FIG. 1, the thermoelectric device related to the present invention comprises the thermoelectric modules, which are the thermoelectric element 1, the counter element 3 countered each other, and the solder layer 5 to adhere the thermoelectric element 1 and the counter element 3 each other.

[0025] The counter element 3 comprises a pair of insulative ceramic substrata (material: alumina) 30, 31 having the planes 30c, 31c for mounting the elements countered each other and the conductive electrodes (material: copper) 35 lain between said planes 30c, 31c and the solder layer 5.

[0026] The solder 5 is composed of conductive, and low melt point metal. The solder 5 is composed of tin-antimony alloy.

[0027] The thermoelectric material for the thermoelectric element 1 converts electric energy into heat energy, or heat energy into electric energy, and the material is composed of one of selected from bismuth-tellurium series, bismuth-selenium series, antimony-tellurium series, and antimony-selenium series. The aforementioned thermoelectric material has naturally poor wetting property against the solder when soldering. Furthermore when used for the thermoelectric device, the solder's ingredient composed of the solder layer 5 is apt to spread into the inside of the thermoelectric element 1 by heat-influences. If the thermoelectric device is used for long time, the spread brings the degradation of the thermoelectric element 1 and the conductive defect.

[0028] According to the present invention, in order to improve the characteristic of soldering and prevent the degradation of the thermoelectric element 1 due to the spread of the solder's ingredient, the restraining layer 7 lies between the thermoelectric element 1 and solder layer 5 as shown in FIG. 2 to prevent the solder's ingredient consisting the solder layer 5 from spreading into the inside of the thermoelectric element 1.

[0029] The restraining layer 7 related to the present invention comprises two-layer composition of the first layer 71 (the average thickness: 0.5 to 10.0 &mgr;m) and the second layer 72 (the average thickness: 0.1 to 1.0 &mgr;m). The first layer 71 has the conductive characteristic, and a main object of the first layer 71 is to prevent the solder's ingredient of the solder layer 5 from spreading into the inside of the thermoelectric element 1. Furthermore, the first layer 71 lies between the end face 1a of the thermoelectric element 1 and the second layer 72 so that it counters directly to the plain end face 1a of the thermoelectric element 1 which is the physical object to be prevented from the spreading phenomenon. Specifically, the first layer 71 comprises the non-electrolytic plating layer composed of nickel-phosphorus series. The average of the thickness of the first layer 71 is thicker than that of said second layer 72.

[0030] The second layer 72 has conductive characteristic and an main object of the second layer 72 is to provide better wetting property against the solder layer than said first layer 71 when soldering. Therefore, the second layer 72 lies between the solder 5 and the first layer 71 so that it counters directly to a solder layer 5. Accordingly, the second layer 72 composed of the better wetting property than the first layer 71 against the solder. Specifically, the second layer 72 comprises the non-electrolytic plating layer composed of nickel-boron series.

[0031] As shown in FIG. 1, the distinction of P-type and N-type of each thermoelectric element 1 is labeled as “P”, and “N”. When the thermoelectric device is used, the electrode 35A (35) of one end side is connected to a plus pole of a power supply, and the other end side is connected to a minus pole of power supply through the plural thermoelectric elements including the electrode 35B (35) is connected, so that electric power is fed between the plus pole of and the minus pole of the power supply. Therefore, the substrate 30 of the one side is cooled to be the low temperature side, and the substrate 31 of the other side is heated to be the high temperature side due to the thermoelectric effect of the each thermoelectric element.

[0032] Alternatively, the low temperature and the high temperature sides are reversed when switching the plus pole and the minus pole to feed electric power in the revered direction.

EXAMPLE OF EMBODIMENT

[0033] The thermoelectric device shown in FIG. 1 and FIG. 2 was used for the test piece. The first layer 71 composed of the non-electrode nickel-phosphorus plate layer (phosphorus is 2 to 8 wt %) was laminated on the both end sides la of the thermoelectric element 1 by the first non-electrode plating procedure. Furthermore, the first layer 72 composed of the non-electrode nickel-boron plate layer (boron is 1 wt %) was laminated on the first layer 71 by the second nonelectrode plating procedure.

[0034] The three kinds of the first layer 71 were prepared for the evolution with the thickness of 0.5 to 1.0 &mgr;m, 1.0 to 5.0 &mgr;m and 5.0 to 10.0 &mgr;m. The two kinds of the second layer 72 were also prepared with the thickness of 0.1 to 0.5 &mgr;m and 0.5 to 1.0 &mgr;m.

[0035] In order to evaluate the defect of soldering, the burn-in test which fed electric current of 2 [A] to each test piece was performed. After the burn-in test the cool-heat test was performed to hold the test pieces at the temperature of −40° C., for 15 minutes and at the temperature of 80° C. for 15 minutes. The variation ratio of inner electrical resistance of the test pieces were measured before and after the burn-in test and the cool-heat test. If the alteration ratio of inner electrical resistance is not more than 0.5%, the test piece is evaluated as an acceptable product. If the alteration ratio of inner electrical resistance exceeds 0.5%, the test piece is evaluated as an acceptable product. 30 test pieces were prepared, and the rate of occurrence for non-acceptable product among thirty (30) test pieces were calculated.

[0036] Furthermore, the other test pieces were tested by the high temperature exposure test to maintain the temperature the test pieces at 150° C. Accordingly, the variation ratio of inner electrical resistance of the test pieces were measured before and after the high temperature exposure test. If the alteration ratio of inner electrical resistance is not more than 10%, the test piece is evaluated as an acceptable product. If the alteration ratio of inner electrical resistance exceeds 10%, the test piece is evaluated as a non-acceptable product. 22 test pieces were prepared, and the rate of occurrence for non-acceptable product among 22 test pieces were calculated.

[0037] Table 1 shows results of the evaluation concerning the embodiment examples.

[0038] In the same way as the present embodiment example, as the test piece related to the comparative example 1, the first layer 71 composed of the non-electrode nickel-phosphorus plate was laminated with the thickness of 1.0 to 5.0 &mgr;m on the end side of the thermoelectric element 1. The thermoelectric device was produced as the same way as above-mentioned, and was evaluated as the same way as the above-mentioned test example. As the test piece related to the comparative example 2, the first layer 71 composed of the non-electrode nickel-phosphorus plate was laminated with the thickness of 0.5 to 1.0 &mgr;m on the end side of the thermoelectric element 1. The thermoelectric device was produced as the same way as above-mentioned, and was evaluated as the same way of as the above-mentioned test example.

[0039] Regarding the test pieces of the comparative example 1 and the comparative example 2, the first layer 71 composed of non-electrode nickel-phosphorus plate was laminated, but the second layer 72 composed of non-electrode nickel-boron plate was not laminated.

[0040] Table 1 shows results of the evolution concerning the comparative example 1 and the comparative example 2.

[0041] Regarding the test piece related to the embodiment example, the second layer 72 composed of the nonelectrode nickel-boron plate layer with good wetting property against the solder is laminated on the first layer 71 composed of the non-electrode nickel-phosphate plate layer with the high spread prevention property. Therefore, this embodiment example had the spread property to prevent solder's ingredient from spreading into the inside of the thermoelectric element 1, and had improved soldering characteristic for electrode 35 and thermoelectric element 1, and had restrained degradation of the test piece after each test.

[0042] Consequently, as understood in Table 1, according the test pieces from the embodiment example, the rate of occurrence of defective test pieces were zero or extremely low.

[0043] As shown in Table 1, under the aforementioned test condition, when the thickness of the first layer 71 was 0.5 to 1.0 &mgr;m, the rate of occurrence of defective test pieces after the high temperature exposure test was {fraction (3/22)} (three per twenty-two). Considering this result, under the aforementioned test condition, the preferable thickness of the first layer 71 is no less than 1.0 &mgr;m. Furthermore, if the test condition of the thermoelectric device is loosened, the thickness of the first layer 71 of no more than 1.0&mgr; is satisfied as a non-defective test piece.

[0044] According to the present invention, when the first layer is a non-electrolytic plating layer composed of nickel-phosphorus series, and the second layer is non-electrolytic plating layer composed of nickel-boron series, the present invention is able to achieve the good effect.

[0045] According to the present invention, when the average thickness of the first layer is thicker than that of said second layer, the solder's ingredient is effectively prevented from spreading into the thermoelectric element. Specially, when the average thickness of the first layer composed of nickel-phosphorus series is thicker than that of the second layer composed of nickel-boron series, the present invention may efficiently achieve the spread prevention effect, may increase the productivity and may achieve low cost in manufacturing due to the thin non-electrolytic plating layer composed of nickel-boron series whose plating speed is slow and expensive in manufacturing. 1 TABLE 1 Comparative Comparative Embodiment example Example 1 Example 2 Second layer Ni—B Thickness (&mgr;m) 0.1˜0.5 0.5˜1.0 — — First layer Ni—P Thickness (&mgr;m) 0.5-1.0 1.0-5.0 5.0-10.0 0.5-1.0 1.0-5.0 5.0-10.0 1.0-5.0 0.5-1.0 Defect ratio after the burn- 0/30 0/30 0/30 0/30 0/30 0/30 4/30 5/30 in test and the cool-heat test High temperature exposure 3/22 0/22 0/22 0/22 0/22 0/22 0/22 9/22 test Defect ratio after 30-hours High temperature exposure 0/22 0/22 0/22 0/22 0/22 0/22 0/22 2/22 test Defect ratio after 10-hours

Claims

1. A thermoelectric device comprising:

a thermoelectric element composed of principally thermoelectric material, a counter element adhered to said thermoelectric material,

a solder layer lying between said thermoelectric element and said counter element and adhering said thermoelectric element to said counter element, a restraining layer to prevent solder's ingredient of said solder layer from spreading into said thermoelectric element,

wherein said restraining layer comprising a first layer to prevent said solder's ingredient of said solder layer from spreading into said thermoelectric element and a second layer composed of material which gets wetter than said first layer against said solder layer.

2. A thermoelectric device according to

claim 1: wherein said first layer is a non-electrolytic plating layer composed of nickel-phosphorus series, and said second layer is non-electrolytic plating layer composed of nickel-boron series.

3. A thermoelectric device according to

claim 1: wherein the average of the thickness of said first layer is thicker than that of said second layer.

4. A thermoelectric device according to

claim 2: wherein the average of the thickness of said first layer is thicker than that of said second layer.